<p>Our increased ability to model and measure a wide variety of phenomena has left us awash in data. In the immediate future, the authors anticipate collecting data at the rate of terabytes per day from many classes of applications, including simulations running on teraflop-class computers and experimental data produced by increasingly more sensitive and accurate instruments such as telescopes, microscopes, particle accelerators, and satellites. Generating or acquiring data is not an end in itself but a vehicle for obtaining insights. While data analysis and reduction have a role to play, in many situations we achieve understanding only when a human being interprets the data. Visualization has emerged as an important tool for extracting meaning from the large volumes of data that scientific instruments and simulations produce. The authors describe an online system that supports three-dimensional tomographic image reconstruction--and subsequent collaborative analysis--of data from remote scientific instruments.</p>